Isoflavone is also called as phytoestrogen because it has a similar function to the female hormone, estrogen. Isoflavone has been reported to have various physiological activities such as prevention of osteoporosis, anticancer activity especially for breast cancer and prostate cancer, lowering cholesterol, antioxidation and the like (Toda T. et al., Food and Development, 31(6), 44˜47, 1996; Murphy P. A., Food Technol., 36, 60˜64, 1982; Adlercreutz. C. H. et al., J. Nutr., 125(3S), 757˜770, 1995).
Genistein, daidzein and glycitein are typical isoflavones, which have been known to exist in leguminous plants, arrowroot and some other plants. So, a lot of studies on methods for preparing plant extracts containing isoflavone have conducted.
A method for preparing a plant extract containing isoflavone using soy beans as a raw material has been mainly studied. For example, Korean patent No. 388511 discloses a method for preparing a soy bean extract containing isoflavone, which is characterized by the steps of extracting soy beans using aliphatic alcohol or the mixture of aliphatic alcohol and water, concentrating the extract, treating the concentrate with aliphatic carbohydrate and extracting it again using aliphatic alcohol. Korean patent publication No. 2001-47621 discloses a method for preparing a soy bean extract containing isoflavone, which is characterized by the steps of adding hexane to crushed soy beans, removing lipid components by perfusive extraction, adding aqueous solution of methanol to the remnants for further perfusive extraction, filtering, concentrating under a reduced pressure and vacuum drying. Also, Korean patent No. 348148 discloses a Puerariae Radix extract containing isoflavone which is prepared by dipping Puerariae Radix in aqueous solution of alcohol, filtering, freezedying and hydrolyzing with acid or base.
Meanwhile, in order to prepare an extract containing isoflavone in higher concentration, it is required to secure a new isoflavone source or to develop an optimum method of extraction.